This invention is related to a system and a method for recycling sulfur hexafluoride (SF6) gas and carbon dioxide (CO2) gas which are used in gas-insulated electric devices and, a sulfur hexafluoride supplying system.
Main global warming gases used in electric power supply industry include carbon dioxide gas exhausted from power generation plants and sulfur hexafluoride gas used as electric insulating medium in high voltage substations.
Emission of carbon dioxide has been increasing due to increase of energy consumption of energy accompanied by development of information technology and people's seeking for comfort. Electric power industry exhausts carbon dioxide gas mainly through thermal electric power generation plants. Various methods for collecting carbon dioxide have been studied, and various methods have been proposed including chemical adsorption method using amine, physical method such as molecular adsorption method, and method using absorption material of complex oxide.
On the other hand, sulfur hexafluoride gas is known to be extremely stable, inert, colorless, odorless, harmless and unburnable. Therefore, sulfur hexafluoride gas is used for various purposes such as electric insulation in electric power devices, etching in semiconductor production process, aluminum refining, noise insulation, electron beam accelerators, shoe soles and shock absorbers. Especially, application of sulfur hexafluoride gas to electric power devices utilizing its good electric insulation characteristics has rapidly prevailed as a key technology to respond to electric power demand recently. Typical electric devices utilizing sulfur hexafluoride gas as insulation medium include gas-insulated switchgears (GISs).
However, sulfur hexafluoride gas is accused of having a high global warming potential—23,900 times higher than carbon dioxide gas. Therefore, the electric power supply industry promotes collecting and recycling sulfur hexafluoride gas, and makes efforts to suppress emission of the sulfur hexafluoride gas to the atmosphere. Besides, alternative gas that can be substituted to sulfur hexafluoride gas as insulation gas of harmless to the environment is searched for.
As a countermeasure of global warming, emission of global warming gas should be suppressed globally. According to “SF6 Gas Handling Standard for Electricity”, Electric Technology Research Association, Vol. 54, No. 3, Dec. 21, 1998, Japan, total amount of sulfur hexafluoride gas that is used as electric insulation medium in electric power devices in Japan was 6,400 tons in 1995. Since the sulfur hexafluoride gas used for electric power devices is confined in sealed tanks, emission to the atmosphere is limited during normal operation. However, in a long range perspective, the newly produced gas will be emitted to the atmosphere in the end, if the gas is not decomposed. Therefore, ultimate solution to the global warming would be minimizing new production of the gas.
Decomposition of sulfur hexafluoride gas theoretically possible by overheating decomposition. However, it is not practical to decompose sulfur hexafluoride gas today because it requires a large amount of energy. The electric power supply industry produces 2,400 tons of sulfur hexafluoride gas in a year in Japan, although the electric power supply industry is trying to collect and recycle the gas. Therefore, reduction of new production of sulfur hexafluoride gas is important to prevent global warming.
Amount of order of hundred million tons of carbon dioxide gas is emitted from electric power generation plants in 1995 in Japan. On the other hand, gas manufacturers newly produce and supply carbon dioxide gas to industries that need it.
Thus, carbon dioxide gas and sulfur hexafluoride gas are newly produced and emitted to the atmosphere, which adversely affects global warming.